I’m leaving a startup. How much co-founder equity should I get?

Question: (org. on Quora)

As a grad student, I worked 5M part-time (25% of total time) with a co-founder, who came up with, funded and executed the idea. We were supposed to split 50/50 if I become full-time. However, we missed a  milestone & I’m leaving to look for a full-time job. We never had a formal discussion with a contract, details on vesting schedule, etc.
I want to be compensated in equity for the work I put in. How much equity should I ask? What % equity is fair?

Answer (by Dan Walter)

culture. Learn more at www.performensation.com. My expertise includes equity compensation programs.